SQL JOIN vs. IN: Which Query Performs Better?

Performance comparison between SQL JOIN and IN

In database queries, both JOIN and IN can be used to retrieve data by comparing values ​​between tables. However, their performance characteristics vary depending on various factors.

Performance Difference

JOIN and IN are fundamentally different query types. JOIN performs a Cartesian product join between specified tables, while IN filters tables based on a set of values ​​obtained from a subquery. Therefore, performance impact may vary:

• JOIN: JOIN is more computationally intensive due to the large number of possible combinations that need to be evaluated. Join columns generally perform better when they are indexed or have unique constraints.
• IN: IN queries are generally faster when the result set of the subquery is relatively small. If the subquery retrieves a large number of values, performance may degrade.

Database Server Considerations

The performance of JOIN and IN is also affected by the specific database server used. For example, in Microsoft SQL Server:

• JOIN with unique or indexed columns: When the join column is unique or has an index, SQL Server can optimize the JOIN query to use indexed lookups, which can significantly improve performance.
• DISTINCT JOIN: If the JOIN columns are not unique, SQL Server may use a DISTINCT JOIN, which filters the results of the subquery before joining the results. This may slow down the query compared to using IN.

Conclusion

While IN may be faster for smaller subquery result sets, JOIN generally performs better with indexes or unique join columns. The best approach depends on the specific query and database server configuration. Consider using an execution plan analyzer or performing performance testing to determine the best option for your specific situation.

More resources

• [IN vs. JOIN vs. EXISTS](https://www.php.cn/link/10b2b8698ea0385652248b0a93b86a57)

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